Geology Reference
In-Depth Information
Winonaite
11.3 g
Found December 16,1994
2.4 × 2.3 × 0.8 cm
Weathering = C
Winonaites are a small group of primitive achondrites with roughly chon-
dritic mineralogy and major element chemistry. Some winonaites contain
relict chondrules, and the group is related to silicate inclusions in iAB iron
meteorites as suggested by their oxygen isotope compositions.
10
Tierra Blanca
8
4
Terrestrial mass
fractionation
Xol/Xpx = 100
Xol/Xpx = 10
Winoma
6
3
Mt. Morris (Wis.)
4
2
Winonaites
Y-74025
lAB Irons
Y-8005
Y-75300
IIICD Irons
2
1
Acapulcoites
Y-75305
Lodranites
Pontlyfni
QUE94535
Aubrites
Brachinites
Y-75261
0
0
0
1
2
3
Fa mol%
4
5
6
2
4
6
8
∂
18
O (‰)
Plate 38
MiNERALogy
SigNiFiCANCE
QUE 94535 is composed of a fine granular aggregate
(0.02 mm grain size) of olivine (Fa
1-3
) and pyroxene (Fs
1-2
)
with a few coarser areas (possibly vestigial chondrules);
about 20% nickel-iron metal and troilite are present, with
much of the metal as thin veinlets throughout the section.
The nickel-iron metal contains 0.1%-0.2% Si.
QUE 94535 is the only winonaite in the U.S. collection,
and because the number of meteorites defining this group
is small, it has been an important sample. Although it is
quite different in texture and mineral composition than
Winona, it shares some common features with the
yamato Antarctic winonaites from the 1974, 1975, and
1980 seasons (right, [250]), and together with other win-
onaites provided a link to the iAB and iiiCD irons (left,
[250]). Like lodranites and acapulcoites, the winonaites
represent partial melting products of a chondrite pre-
cursor that is unknown among our collections. Therefore,
this small group lies at the center of our understanding of
melting processes in the early solar system.
References [250, 251]
